1. Field of the Invention
This invention relates to ultrasonic motors and more particularly to a two-dimensionally driving ultrasonic motor using as a vibration source such electro-mechanical converting device as a piezo-electric device.
2. Related Background Art
Recently, in such drive source as of an analyzing apparatus, semiconductor related apparatus or optical apparatus is required a three-dimensional direction positioning of high precision and speed. As a required of high speed and high precision actuator. Such so-called electro-mechanical energy converting device as a piezo-electric device or electro-striction device is noted today.
Now, as a two-dimensionally positioning and moving apparatus is recently noted a so-called ultrasonic motor which is superior to the conventionally used electromagnetic motor in the following points:
(1) It is small in size, light in weight and low in power consumption;
(2) A low speed and high torque are obtained without needs for a reduction gear;
(3) The number of parts is low, assembly is easy and the reliability is high;
(4) No magnetic influence is given or received; and
(5) There is no backlash and positioning is easy.
Thus, various techniques are being studied and developed to utilize these advantages.
Generally, ultrasonic motors can be largely divided into a rotary driving type and linear driving type.
Now, there is suggested such linear driving type ultrasonic motor as is mentioned, for example, in Japanese patent application laid open No. 7875/1990.
This linear driving type ultrasonic motor comprises two pairs of piezo-electric devices, a laminated piezo-electric member made by laminating many plate-like piezo-electric devices and an upper stand and lower stand made respectively of metals or the like bonded respectively to the upper surface and lower surface of the piezo-electric member. The two pairs of piezo-electric devices are bonded through an insulating member so that either pair may be the same in the direction of the polarization. The two pairs of piezo-electric devices and the laminated piezo-electric member are connected to respective independent driving voltage applying lead wires.
The ultrasonic motor of the above mentioned formation vibrates the laminated piezo-electric member and the piezo-electric devices fitted to the member so that, by the synthesized vibration in the horizontal and vertical directions generated thereby, the mass point on the vibrator may make an elliptic vibration of any size and manner. Therefore, when a driven member is contacted with the upper surface of the vibrator, the driven member will be driven two-dimensionally.
In the ultrasonic motor mentioned in the above mentioned publication of Japanese patent application laid open No. 7875/1990, there are defects that, as a vibration in the horizontal direction is generated in the vibrator by the two pairs of piezo-electric devices, a high driving voltage will be required and the amplitude of the horizontal vibration will not be able to be made so large.
Further, as of an ultrasonic motor actuator, there are suggested the publications of Japanese patent application laid open Nos. 15572/1986, 141980/1987, 264543/1987 and 315269/1989.
However, the conventional technique disclosed in the above mentioned publication of Japanese patent application laid open No. 15572/1986 has problems that the resonant frequency of the bending vibration of the vertically rising part of the elastic body and the resonant frequency of the bending vibration of the horizontal part of the elastic body will have to be made to coincide with each other, the dimensions will have to be changed by trial errors, a trial make will have to be repeated, much labor will be required and the shape will be T and will have to be large.
Also, the conventional technique disclosed in the above mentioned publication of Japanese patent application laid open No. 141980/1987 has problems that, in the ultrasonic vibrator, in order that the resonant frequency of the bending and the resonant frequency of the extension and contraction may be made to coincide with each other, the dimensions will have to be changed by trial errors, a trial make will have to be repeated and much labor will be required and, the same as in the one in the above mentioned publication of Japanese patent application laid open No. 15572/1986, in case an ultrasonic elliptic vibration is generated by combining a different mode (resonant mode), by the variation of the size of the pressing contact force of the driven body held in contact there and the temperature rise of the vibrator, the resonant frequencies of both modes will be delayed to be different and the practice will be difficult.
Further, the conventional technique disclosed in the above mentioned publication of Japanese patent application laid open No. 264543/1987 has problems that the moving element is a cylindrical body consisting of a piezo-electric device and the applied voltage will have to be large, in case the bending vibration of the moving element is used by the resonant vibration, as the cylindrical body is a hollow cylinder, the number of the vibrations will enter an audible region and noises will be generated and, further, in order to elevate the driving capacity, in case the bending vibration and extending and contracting vibration are both used in the resonant frequency, the frequencies will have to be made to coincide with each other the same as in the ones in the above mentioned publications of Japanese patent application laid open Nos. 15572/1986 and 141980/1987.
Also, the conventional technique disclosed in the publication of Japanese patent application laid open No. 315269/1989 has a problem that, as a sliding vibrator is used for the piezo-electric body of the vibrator and is used in non-resonance, a large voltage will have to be applied to obtain a vibration amplitude.